Re: [PATCH 0/3] iopmem : A block device for PCIe memory

[Sagi Grimberg]

> > You do realise that local filesystems can silently change the
> > location of file data at any point in time, so there is no such
> > thing as a "stable mapping" of file data to block device addresses
> > in userspace?
> >
> > If you want remote access to the blocks owned and controlled by a
> > filesystem, then you need to use a filesystem with a remote locking
> > mechanism to allow co-ordinated, coherent access to the data in
> > those blocks. Anything else is just asking for ongoing, unfixable
> > filesystem corruption or data leakage problems (i.e.  security
> > issues).
>
> And at least for XFS we have such a mechanism :)  E.g. I have a
> prototype of a pNFS layout that uses XFS+DAX to allow clients to do
> RDMA directly to XFS files, with the same locking mechanism we use
> for the current block and scsi layout in xfs_pnfs.c.

Christoph, did you manage to leap to the future and solve the
RDMA persistency hole? :)

e.g. what happens with O_DSYNC in this model? Or you did
a message exchange for commits?